The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
With the rapid development of Internet technology, large amounts of multimedia services have emerged, among them some application services requiring that multiple users receive the same data at the same time, namely multicasting the data, and such application services include video on demand, television broadcasting, video conference, online education, interactive games and so on.
Multicast service is the technique that can transfer the data from a data source to multiple destinations, including multicast and broadcast. As to broadcast service, in traditional mobile networks, Cell Broadcast Service (CBS) only allows transferring low speed data to all users through the shared broadcast channel of the cell, which belongs to message services. As to multicast service, there has been IP multicast technique in terms of existing IP network, but the mobile network has special network structure, function entities and wireless interfaces, which are different from those of IP network, so current IP multicast techniques are only applicable for cable IP networks while not applicable for mobile networks. In addition, compared with common services, mobile multimedia services have the characteristics such as large quantity of data, long time of duration, sensitive time delay and so on. Therefore, transmission techniques of current broadcast services and multicast services are not applicable for data transmission of mobile multimedia services.
In order to utilize mobile network resources effectively, on one hand, a Wide Code Division Multiple Access/Global System for Mobile Communications (WCDMA/GSM) global standardization organization, the Third Generation Partnership Project (3GPP), put forward Multimedia Broadcast/Multicast Service (MBMS), and Multicast and Broadcast Service (MBS) is introduced into the latest protocol IEEE802.16e/D5 by the Institute of Electrical and Electronics Engineers (IEEE) 802.16. MBMS and MBS provide the specifications of transferring the data from one data source to multiple users in the mobile network, so that the mobile network can provide point to multipoint service of transferring the data from one data source to multiple users, thereby network resources can be shared, utilization ratio of network resources is increased, and especially utilization ratio of idle interface resources is increased too. The newly provided MBMS and MBS cannot only implement multicast and broadcast of low speed messages such as plain text, but also that of high speed multimedia services, and this is obviously in trend of future mobile data development.
The network structure of MBS put forward by IEEE802.16 protocol is as shown in FIG. 1. In FIG. 1, MBS server, a mobile network function entity, is added to support MBS, MBS server acts as the entry to content providers on one hand, and on the other hand, MBS server manages multicast data transmission of underlying Base Stations (BS) as well as distributes the multicast data to the underlying BS. In addition, the function entities, such as Mobile station (MS), BS and so on, need to be enhanced by adding service functions associated with MBS service.
MBS operations mainly include the following parts: obtaining the list information of MBS, authenticating MBS and obtaining the encryption key of MBS, and receiving the MBS normally. Specifically speaking, before normally receiving MBS service, MS acquires information like MBS content list etc. from MBS server firstly, and then requests BS to authenticate the receiving of MBS content; if the authentication is passed, BS transmits information including MBS downlink service parameters and so on to MS, and then MS requests BS to return the key of MBS; upon receiving the downlink service parameters and the key of MBS, MS can receive related Media Access Control Protocol Data Unit (MAC PDU) and receive the MBS service normally.
The procedure of normally receiving MBS service mainly refers to receiving the MBS service content by using the received MBS downlink service parameters. In current standard draft, MBS downlink service parameters mainly include MBS ZONE identifier and Multicast Connection ID (Multicast CID). After the MBS downlink service parameters are obtained, physical resource indication has to be performed for MS during the service reception of MBS so as to implement the reception of MBS content.
In the latest protocol IEEE802.16e/D5 of current IEEE802.16, MBS-MAP message is introduced, which includes Information Elements (IEs) as shown in table 1.
TABLE 1SyntaxSizeNotesMBS-MAP_Message_Format( ){Management Message Type8 bits= ?Frame number24 bits The frame number is identical to theframe number in the DL-MAPfor (i = 0; i < n; i++) {Multicast CID12 bits 12 LSB of CID for multicastModulation and Coding4 bitsmode (DIUC)OFDMA Symbol offset8 bitsOFDMA symbol offset with respect tostart of the MBS zoneSubchannel offset6 bitsPower Offset (Boosting)3 bits000: normal (not boosted); 001: +6dB;010: −6dB; 011: +9dB; 100: +3dB;101: −3dB; 110: −9dB; 111: −12dB;No. OFDMA Symbols7 bitsNo. Subchannels6 bitsRepetition Coding2 bits0b00 - No repetition codingIndication0b01 - Repetition coding of 2 used0b10 - Repetition coding of 4 used0b11 - Repetition coding of 6 usedNext MBS frame offset8 bitsThe Next MBS frame offset value islower 8 bits of the frame number inwhich the BS shall transmit the nextMBS frame.Next MBS OFDMA Symbol8 bitsThe offset of the OFDMA symbol inoffsetwhich the next MBS zone starts,measured in OFDMA symbols fromthe beginning of the downlink framein which the MBS-MAP istransmitted.}if !(byte boundary) {Padding Nibble4 bitsPadding to reach byte boundary.}}
MBS-MAP message is used to notify the physical channel resource allocated for specific Multicast CID in the given MBS ZONE. MBS-MAP message provides the modulation and coding mode (which is indicated by Downlink Interval Usage Code (UIDC)) and power offset (which is indicated by Boosting), which are used in the given physical channel resource (i.e. Burst), and position of the next service frame of MBS. Therefore, if only MBS-MAP message can be correctly detected, according to this message, MS can obtain the physical channel resource corresponding to the multicast connection, get the modulation and coding mode and power offset etc, which are used in this physical channel resource, and determine position of the next MBS frame including this multicast connection, thereby normally receive the data through the multicast connection. Therefore, while receiving the MBS service, MS can implement physical resource indication through the MBS-MAP message.
Due to the above-mentioned reasons, MS has to determine position of the MBS-MAP message when MS is receiving the MBS service initially or the service reception of MBS is desynchronized due to poorer channel quality. IEEE802.16e/D5 protocol offered one implementing mode, which is to introduce an IE, i.e. an MBS-MAP IE (MBS-MAP_IE( )) to indicate position of the MBS-MAP message, into the Downlink channel Map (DL-MAP). The structure of this MBS-MAP_IE( ) is as shown in FIG. 2. If MS detects that the MBS ZONE identifier and Multicast CID included in this IE are identical to those of the MBS service expected to be received by this MS, the MS can receive the associated MBS-MAP message at the corresponding OFDM Symbol Offset.
TABLE 2SyntaxSizeNotesMBS_MAP_IE {Extended DIUC4 bitsMBS_MAP = 0x05Length4 bitsLength = 0x03 Multicast CID12 bits 12 LSB of CID for multicastMBS ZONE identifier7 bitsMBS ZONE identifier corresponds to theidentifier provided by the BS at connectioninitiationOFDMA Symbol offset8 bitsThe offset of the OFDMA symbol in whichthe MBS zone starts, measured inOFDMA symbols from the beginning ofthe downlink frame in which the DL-MAPis transmitted. Macro diversity enhanced1 bits0 = Non Macro-Diversity enhancedzone1 = Macro-Diversity enhanced zoneIf (Macro diversity enhanced== 1){Permutation2 bits0b00 = PUSC permutation0b01 = FUSC permutation0b10 = Optional FUSC permutation0b11 = Adjacent subcarrier permutationID cell6 bits}else {Reserved8 bits}}
It can be seen from table 2 that, only the OFDMA symbol offset, in which the MBS zone starts, is the position information of MBS-MAP message in the MBS-MAP_IE( ). As to MBS-MAP message, if just the MBS-MAP_IE( ) in DL-MAP message is indexed, because the practical physical channel resource occupied by the MBS-MAP message cannot be determined only by the information of the OFDMA symbol offset in which the MBS zone starts, thus the physical channel resource occupied by MBS cannot be determined, and then the service reception of MBS cannot be implemented.